JP2002260274A - Phase changing optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium that can reduce cross write caused by the thermal interference of the adjacent track by providing a region which maintains amorphous state regardless of write and erase between the tracks of a phase change recording optical recording medium in the method to overcome the cross write problem caused by the thermal interference when making high density recording on a phase change recording optical recording medium. SOLUTION: The constitution in this invention is featured in that the optical recording medium has a guard band region between recording tracks to maintain amorphous state in a phase change recording optical recording medium that utilizes the change in crystalline structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly, to a phase change type optical recording medium characterized by a track-to-track configuration of the phase change type optical recording medium.

[0002]

2. Description of the Related Art In recent years, a phase-change type optical recording medium has been
It has been put to practical use as a W, DVD-RAM, DVD-RW, etc., and is widely used for computer data files, video recording, and the like.

When laser light is focused on the disk surface and quenched by controlling the pulse time and power,
It becomes amorphous and does not become a recording mark, and when cooled slowly, it becomes a crystalline state and becomes an erased state. As described above, recording using light is essentially thermal recording. In the reproduction, the reflectivity changes due to the difference in the reflectance and the phase between the crystal and the amorphous, and the reproduction can be performed.

In order to record more data on a phase-change optical disk, it is necessary to shorten the mark pitch of recording marks and the track pitch.
It is possible to shorten the mark pitch to some extent by shortening the pulse width of the recording pulse, performing recording with finer multi-pulses, and speeding up the rising and falling of the recording pulse. The flow of heat in the direction along the track can be controlled to some extent by pulses.

On the other hand, the flow of heat in the direction of the track pitch cannot be controlled by light pulses. The bleeding of heat is free due to the heat conduction of the film. Therefore, when recording is performed, the recording mark of an adjacent track is affected by the thinning. Repeated recording has a problem that errors in adjacent tracks increase. In order to prevent this, the only known method is to increase the depth of a groove provided for tracking.

However, the groove depth has an optimum value for optical reasons and cannot be determined only by thermal design. Further, the groove depth for preventing thermal interference needs to be considerably large, and there is a problem that it is difficult to form a substrate.

[0007]

SUMMARY OF THE INVENTION The present invention solves these problems and provides an area between tracks for maintaining an amorphous state irrespective of recording / erasing when using a phase change type optical recording medium. Accordingly, it is possible to provide a phase change type optical recording medium capable of reducing cross writing caused by thermal interference with an adjacent track when performing high density recording on the phase change type optical recording medium.

[0008]

The above object of the present invention is achieved by the following means. According to the present invention, claim 1
Is characterized in that a phase change type optical recording medium utilizing a change in crystal structure has a guard band region for maintaining an amorphous state between recording tracks.

Second, the optical recording medium according to the first aspect is characterized in that the phase-change recording layer is made of a material based on a metastable phase of Sb ₃ Te.

Third, in the optical recording medium according to claim 2, the composition ratio of the phase-change recording layer is a material in which the content of additional elements other than SbTe in the total amount of elements is within 15 at%. It is characterized by.

Fourth, in the optical recording medium according to the second aspect, whether the recording mark is amorphous, the erasing area is crystalline, and the reflectance of the recording mark is higher than that of the erasing area. , Are the same.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS CD-RW, DVD-RW, DV
D + RW and the like are recorded in a groove. Land does not record any signals. When the track pitch of such an optical disk for groove recording is reduced, the lands are kept in an amorphous state.

The DVD-RAM records marks on both grooves and lands. In the case of such an optical disk of land & groove recording, the slope between the groove and the land is in an amorphous state.

A more effective method is that the above-mentioned disk has an amorphous recording mark and a low reflectivity, but uses optical interference to reverse the phase so that the amorphous is highly reflective. So that In this case, the phase change film immediately after the film formation becomes entirely amorphous and has a high reflectance, so that recording and reproduction can be performed by a drive without performing a general crystallization process called initialization. Only recording tracks are recorded and reproduced on the medium in this state. Since there is no laser irradiation between the tracks, the track is inevitably in an amorphous state immediately after film formation.

The thermal conductivity of amorphous and crystalline materials is overwhelmingly greater for crystalline materials. Therefore, the amorphous portion between the tracks functions as a guard band that blocks thermal interference between the tracks due to low thermal conductivity.

In the case of a medium in which the phase is reversed by utilizing optical interference and the amorphous is highly reflective, the phase change film immediately after film formation is entirely amorphous and has a high reflectance. Recording and reproduction can be performed by a drive without performing the entire crystallization process of initialization. When only the recording tracks are recorded and reproduced on the medium in this state, the tracks are not irradiated with the laser, so that they are inevitably in an amorphous state immediately after film formation. The procedure of performing initialization after film formation and then amorphizing between tracks again becomes unnecessary.

The structure of the amorphous phase immediately after film formation, which functions as a guard band, is microscopically different from that of the phase that has undergone an initialization step and has been amorphized again by rapid cooling with laser light, and has a lower thermal conductivity. It is suitable for use as a guard band because of its low crystallization.

Further, the phase change recording layer is made of Sb ₃ such as AgInSbTe, AgInSbTeGe, GeInSbTe or the like.
When a material having a Te-based metastable phase as a skeleton is used, the present invention is more effective. As a practical phase change material,
There are two main types of materials: a material using a Ge ₂ Sb ₂ Te 5 compound composition and a material having a Sb ₃ Te metastable phase as a skeleton. Sb ₃ Te material has a thermal conductivity of Ge ₂ Sb in a crystalline state.
₂ Te ₅ greater than the material the thermal conductivity of the crystalline state of. That is, heat interference is likely. However, in the amorphous phase, the thermal conductivity is extremely low, which is equivalent to that of Ge ₂ Sb ₂ Te ₅ . Therefore, the effect of the guard band is greater.

Further, in order to reduce the thermal conductivity of the Sb ₃ Te group, the content of additional elements other than SbTe in the total amount of the elements must be 1%.
It has been found that the effect is particularly effective when the content is within 0 at (atomic)% (below). Further, when Ag and In are small and Ge is large, it is effective to reduce heat conduction.

FIG. 1 shows the layer structure of the optical recording medium of the present invention. The material of the substrate (1) is usually glass, ceramics,
Alternatively, it is a resin, and a resin substrate is suitable in terms of moldability and cost. Representative examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, and the like. However, a polycarbonate resin and an acrylic resin are preferable in terms of processability, optical characteristics, and the like.

The materials of the first protective layer (2) and the second protective layer (4) are SiO, SiO ₂ , ZnO.S
nO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO,
Metal oxides such as ZrO ₂ , Si ₂ N ₄ , AlN, T
Nitride such as iN, BN, ZrN, ZnS, In
₂ S ₃ , sulfide such as TaS ₄ , SiC, TaC, B ₄
Examples thereof include carbides such as C, WC, TiC, and ZrC, diamond-like carbons, and mixtures thereof. These materials can be used alone as a protective layer, or as a mixture of each other. Further, it may contain impurities as needed. However, the melting point of the heat-resistant protective layer needs to be higher than the melting point of the recording layer, and it is also required that the coefficient of thermal expansion is small and the adhesion is good. In addition, the protective layer can be multi-layered as necessary.

The thickness of the first protective layer is 20 to 250 n.
m, preferably 30 to 100 nm. 20n
When the thickness is smaller than m, the protective function for environmental resistance is reduced, the heat resistance is reduced, and the heat storage effect is reduced, and the protective layer does not function. On the other hand, if the thickness is more than 250 nm, it is not preferable because the film temperature rises in the film formation process, thereby causing film peeling or cracking or lowering the sensitivity during recording. The film thickness can be set so that the reflectance and the modulation are increased within the above range of the film thickness. The optimum film thickness differs depending on the wavelength of the light used. This is because the degree of modulation is amplified using light interference. It is necessary to use a material having a higher refractive index than the substrate in the wavelength region to be used.

If the thickness of the second protective layer is less than 4 nm, the heat resistance basically decreases, which is not preferable. 100n
If it exceeds m, the overwrite characteristics deteriorate due to film peeling, deformation, and a decrease in heat dissipation due to a rise in temperature. The film thickness can be set so that the reflectance and the modulation are large and the heat radiation to the reflective heat radiation layer is good within the above range of the film thickness.
In order to suppress the thermal interference, it is necessary to reduce the thermal conductivity, raise the temperature for forming the recording mark in a short time, and then cool the recording mark as quickly as possible with the reflective heat dissipation layer.

For the recording layer (4), an Sb ₃ Te-based alloy having a predetermined composition is used. The film thickness is 5 to 50 nm, preferably 6
２５25 nm. If it is thinner than 5 nm, it is difficult to form a uniform film, and it will not function as a recording layer. 50 nm
If the thickness is larger, the signal jitter increases, and the repetitive rewriting performance decreases.

As a material of the reflection heat radiation layer (5), Al,
A simple substance or an alloy mainly composed of a metal such as Au, Cu, or Ag can be used. If necessary, a plurality of different metals and alloys may be laminated. It is important for this layer to efficiently release heat, and the thickness is 20 to 250 n.
m. Preferably, it is 30 to 150 nm. If the film thickness is too thick, the heat radiation efficiency is too good and the sensitivity is poor, and if it is too thin the sensitivity is good but the overwrite characteristics are poor. It has high thermal conductivity, preferably 100 W / m
k or more, and a high melting point and good adhesion to the protective layer material are required.

Such a protective layer, a reflective heat radiation layer, and a recording layer are formed by various vapor deposition methods, for example, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam deposition method. And the like. Further, the optical information recording medium of the present invention is not limited to those having various layers as described above, for example, an organic protective film may be provided on a reflective heat dissipation layer, They may be attached with an adhesive.

Since the thermal conductivity of the phase change type recording layer was a small value and was difficult to measure, the electric conductivity was substituted. This is because, in the case of metal, free electrons, which are the same in both heat conduction and electric conduction, are the main components of conduction. According to the measurement, Sb ₃ T
It was confirmed that the electrical conductivity of the e-based alloy thin film differs between the crystal and the amorphous by 5 digits or more. The same was true for the Ge ₂ Sb ₂ Te ₅ compound system. Since the Sb ₃ Te-based material had better electric conductivity as a whole, it is considered that the heat conduction was higher.

(Examples) Next, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited by the following examples.

[0029]Examples 1 to 6 Glue with a diameter of 12cm, thickness of 0.6mm and track pitch of 0.7μm
Dehydrating Polycarbonate Disk Substrate with Probe at High Temperature
After processing, the first protective layer, the recording layer, and the second protective layer are sputtered.
A protective layer and a reflective heat dissipation layer were sequentially formed. As the first protective layer
ZnS / SiO _TwoUse target and make it 80nm thick
Was. The recording layer uses a SbTe-based alloy target with a predetermined composition ratio.
Argon gas pressure 3 × 10^-3Torr, DC power 0.4
Sputtering was performed at kW to a film thickness of 20 nm. Second protective layer
Is ZrO_Two・ SiO_TwoUse target, thickness 15nm
And Ag-1.5at% Cu alloy
And a thickness of 120 nm. Furthermore, reflection
Organic protection made of acrylic UV curable resin on heat dissipation layer
The film is applied to a thickness of 10 μm using a spinner,
I let you. A further 12 cm in diameter and 0.6 mm thick
Laminate the carbonate disc with an adhesive sheet,
Initially crystallizing the recording layer with a semiconductor laser to produce an optical recording medium
Body.

Thereafter, the disk was rotated at a linear velocity of 12 m / s while irradiating 10 mW of DC light with a drive using a pickup having a wavelength of 660 nm and NA of 0.65, and all lands were made amorphous. For recording / reproducing, the wavelength 660n
m, a pickup with NA of 0.65 was used. The recording method used was a pulse modulation method, and the modulation method was an EFM + modulation method. The ratio of recording power / erasing power is about 1.8 to 2.
The reproduction power was set to 0.7 mW. The linear density was 0.267 μm / bit, and overwriting was performed under the same conditions. Jitter is data to clock
k was measured, and recording and reproduction were all performed at 3.5 m / s. The disk of Example 1 having a recording layer of Ge ₂ Sb ₂ Te ₅ was evaluated at a linear density of 0.4 μm / bit. This is 0.
At a recording density of 267 μm / bit, the initial jitter is 1
This is because the error reaches about 6% and an error starts to occur. G
The thermal conductivity of the e ₂ Sb ₂ Te ₅ recording layer is smaller than that of the Sb ₃ Te-based recording layer. Therefore, heat bleeding in the track pitch direction, such as cross writing and cross erasing, is originally small. However, it is vulnerable to linear thermal interference, and it is difficult to increase the recording density.

The heat shielding region of the present invention is Ge ₂ Sb ₂ Te ₅
Although it is effective for a system disk, it is difficult to increase the linear density as described above, and therefore, the recording layer is more preferably an Sb ₃ Te system. The evaluation item is cross erase. Five tracks are recorded and the third track in the middle is overwritten 1000 times. At this time, the average value of the increase in the jitter of the second and fourth tracks as the adjacent tracks was observed. Table 1 shows the results. Jitter is the data to data when recording is performed with the recording strategy and recording power optimized for each embodiment.
This is a value σ / Tw obtained by normalizing the clock jitter σ with the window width Tw.

[0032]

[Table 1]

Example 7 This is a case where the crystalline region of the recording layer has a low reflectance and the amorphous region has a high reflectance. A land and groove recording polycarbonate disk substrate having a diameter of 12 cm, a thickness of 0.6 mm, and a track pitch of 0.6 μm is dehydrated at a high temperature, and then is translucent metal layer, a first protective layer, a recording layer, a second protective layer, A reflective heat dissipation layer was formed sequentially. The film was formed by magnetron sputtering. Here, the land & groove recording substrate having a track pitch of 0.6 μm means that the groove pitch is 1.
The substrate is 2 μm, with grooves and lands occupying half each. Ag-1wt% Pd as translucent metal layer on substrate
-0.9wt% Cu 15nm, ZnS-Si as first protective layer
O ₂ is 100 nm, and Ag ₁ In ₃ Sb ₆₅ T is used as a recording layer.
e ₂₇ Ge ₄ at% of 17 nm, GeNx-CrNx as the second protective layer
A 16 nm mixed film was formed, and 150 nm of pure Ag was formed as a reflective layer. Thereafter, a disc having a thickness of 1.2 mm was obtained by laminating a 0.6 mm polycarbonate dummy plate using a UV resin.

The disk is immediately recorded by a drive without going through a normal initialization process using a large-diameter laser. This is because the initial recording layer is amorphous and has a high reflectance. For recording / reproducing, wavelength 660 nm, NA 0.65
Pickup was used. The recording method used was a pulse modulation method, and the modulation method was an EFM + modulation method. The recording power / erasing power ratio was set to about 1.8 to 2.2, and the reproducing power was set to 0.7 mW. The linear density is 0.267 μm / bi
t, and overwriting was performed under the same conditions. Jitter measured data to clock, and recording and reproduction were all performed at 3.5 m / s.

The evaluation item is cross erase. The land, groove, land, groove, and land are recorded on five tracks, and the third track in the middle is overwritten 1000 times. At this time, the average value of the increase in the jitter of the second and fourth tracks, which are the adjacent tracks, was observed. The jitter rise was 0.5%. Despite the narrow track pitch, the rise in jitter was as small as 1% or less. It is considered that this was effective in that the amorphous phase immediately after the film formation remained at the boundary between the groove and the land and was thermally shielded.

As a comparative example, Table 2 shows a case where the lands were not made amorphous after initialization with respect to the disks of Examples 1 to 6. The cross erase is larger than the embodiment. It can be seen that the cross erase is different due to the difference in heat conduction depending on whether the guard band called a land is crystalline or amorphous, even though it is the same disk.

[0037]

[Table 2]

Further, Table 3 shows Comparative Examples 7 to 10 in which the composition of the recording layer was such that the additive element was 15 at% or more. In this case, although the land was made amorphous, the thermal conductivity became too large in terms of the composition of the recording layer, and the cross erase became large. When the amount of the added element increases with respect to the parent phase of Sb and Te, the increase in jitter is large. Even in these compositions, the heat conductivity of an amorphous material is the same as that of a crystal, but the original heat conductivity is large, so that heat bleeding is too large. In addition, it is considered that the increase of In is particularly caused by a remarkable increase in the crystallization temperature and an excessively high operation temperature for recording and erasing. Ag does not raise the crystallization temperature, but has a high thermal conductivity of itself. Therefore, if added in a large amount, the thermal conductivity of the recording layer will be too high. Ge
Has a small side effect because it has a small thermal conductivity and has a function of lowering the thermal conductivity when added to the recording film.

[0039]

[Table 3]

[0040]

According to the present invention, there is provided a phase change type optical recording medium utilizing a change in crystal structure, wherein a guard band region for maintaining an amorphous state is provided between recording tracks. According to the invention described in (1), an optical disk suitable for high-density recording can be obtained, in which diffusion of heat bleeding during recording in the track pitch direction can be reduced.

According to the optical recording medium of the present invention, the phase-change recording layer is made of a material based on a metastable phase of Sb3Te. With the use of the recording layer, the recording density in the linear direction could be increased, and higher density recording was possible.

The optical recording medium according to claim 3 is characterized in that the composition ratio of the phase change recording layer is a material in which the content of additional elements other than SbTe in the total amount of elements is within 15 at%. According to the optical disc shown in the optical recording medium, when the recording layer based on Sb3Te is used,
% Or less, the thermal conductivity of the recording layer could be kept small, and a small cross erase was achieved.

In the optical recording medium according to claim 4, the recording mark is amorphous, the erasing area is crystalline, and the reflectance of the recording mark is higher than that of the erasing area. According to the optical disc shown in the optical recording medium, which is the same, signals can be directly recorded by a drive for recording and erasing without going through an initialization step. It can remain crystalline. This eliminates the need to use a drive to form an amorphous portion as a guard band, and that the amorphous phase immediately after film formation has a lower thermal conductivity than the amorphous phase formed by rapid cooling of the laser. Therefore, the cross erase can be made smaller, and as a result, it was possible to adapt to high density recording.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a layer configuration of an optical recording medium of the present invention.

FIG. 2 is a cross-sectional view of an example having a reflective heat radiation layer in the layer configuration of the optical recording medium of the present invention.

Claims (4)

[Claims] 1. A phase change type optical recording medium utilizing a change in crystal structure, wherein a phase change type optical recording medium has a guard band region for maintaining an amorphous state between recording tracks. 2. The phase-change optical recording medium according to claim 1, wherein the phase-change recording layer is made of a material based on a Sb ₃ Te metastable phase. 3. The phase change type optical recording medium according to claim 2, wherein the composition ratio of the phase change type recording layer is SbTe in all elements.
A phase change type optical recording medium characterized by being a material having a content of additional elements other than 15 atomic% or less. 4. The phase-change optical recording medium according to claim 2, wherein the recording mark is amorphous, the erasing area is crystalline, and the reflectance of the recording mark is higher than that of the erasing area. A phase-change optical recording medium characterized by being high or the same.